1. Field of the Invention
The invention relates to a process for operating a fluidized bed reactor.
2. Description of the Related Art
Fluidized bed reactors are used, for example, for preparation of trichlorosilane (TCS) by the reaction of metallurgical silicon with HCl at 350-400° C. It is likewise possible to produce TCS in a fluidized bed reactor from metallurgical silicon with STC/H2 (STC=silicon tetrachloride).
Fluidized bed reactors are also used for production of polycrystalline silicon granules. This is accomplished by fluidization of silicon particles by means of a gas flow in a fluidized bed, which is heated to high temperatures by means of a heating apparatus. As a result of addition of a silicon-containing reaction gas, a pyrolysis reaction proceeds at the hot particle surface. This deposits elemental silicon on the silicon particles and the individual particles grow in diameter. Through the regular removal of grown particles and addition of smaller silicon particles as seed particles (called “seed” later in the document), the process can be operated continuously with all the associated advantages. Silicon-containing reactant gases that have been described are silicon-halogen compounds (e.g. chlorosilanes or bromosilanes), monosilane (SiH4), and mixtures of these gases with hydrogen. Deposition processes of this kind and apparatuses therefor are known, for example, from U.S. Pat. No. 4,786,477 A.
In the disassembly and reassembly of a fluidized bed reactor, oxygen and air humidity get into the reactor interior and the necessarily open pipelines via the surrounding atmosphere.
U.S. Pat. No. 8,017,024 B2 discloses a method for producing polycrystalline silicon granules in a fluidized bed reactor. After the deposition has ended, the reactor interior is cooled, while being purged with an inert gas such as H2, N2, Ar, He or a mixture of said gases. Subsequently, the cooled silicon particles are withdrawn, the reactor is disassembled, the reactor tube is replaced by a new one, the reactor is reassembled, and silicon particles are introduced into the reactor tube. Subsequently, the silicon particles are heated and a new deposition operation begins.
U.S. Pat. No. 6,827,786 B2 also describes a fluidized bed reactor. The intention is to recover energy by contacting the granules with gases having a low level of carbon and oxygen impurities.
The problems described gave rise to the objective of the invention.